Blasphemy against the Holy Spirit is what Jesus called the sin that will not be forgiven: seeing the Spirit's clear witness to Christ and calling it the work of the devil. It is not a careless word; it is a settled, final rejection of the only One who can forgive. The very fear that you have committed it is itself strong evidence that you have not.
Not a summary of these passages: the passages themselves. Read them, then come back to the study below.
The study
What the Scripture says
1
The scene: the Spirit's work called evil
Jesus healed a demon-possessed man by the Spirit of God, and the Pharisees said, 'This man does not cast out demons, except by Beelzebul, the prince of the demons.' Jesus answered that if He cast out demons by the Spirit, 'the Kingdom of God has come upon you.' The religious leaders were not confused; they could see the Spirit's fingerprint on Jesus, and they named it as the devil.
But when the Pharisees heard it, they said, “This man does not cast out demons, except by Beelzebul, the prince of the demons.” Knowing their thoughts, Jesus said to them, “Every kingdom divided against itself is brought to desolation, and every city or house divided against itself will not stand. If Satan casts out Satan, he is divided against himself. How then will his kingdom stand? If I by Beelzebul cast out demons, by whom do your children cast them out? Therefore they will be your judges. But if I by the Spirit of God cast out demons, then the Kingdom of God has come upon you.But when the Pharisees heard it, they said, This fellow doth not cast out devils, but by Beelzebub the prince of the devils. And Jesus knew their thoughts, and said unto them, Every kingdom divided against itself is brought to desolation; and every city or house divided against itself shall not stand: And if Satan cast out Satan, he is divided against himself; how shall then his kingdom stand? And if I by Beelzebub cast out devils, by whom do your children cast them out? therefore they shall be your judges. But if I cast out devils by the Spirit of God, then the kingdom of God is come unto you.
The scribes who came down from Jerusalem said, “He has Beelzebul,” and, “By the prince of the demons he casts out the demons.” He summoned them, and said to them in parables, “How can Satan cast out Satan?And the scribes which came down from Jerusalem said, He hath Beelzebub, and by the prince of the devils casteth he out devils. And he called them unto him, and said unto them in parables, How can Satan cast out Satan?
But if I by the Spirit of God cast out demons, then the Kingdom of God has come upon you.But if I cast out devils by the Spirit of God, then the kingdom of God is come unto you.
The warning: the Spirit's witness rejected is unforgivable
Jesus said, 'every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven men.' Speaking against the Son of Man can be forgiven, 'but whoever speaks against the Holy Spirit, it will not be forgiven him, neither in this age, nor in that which is to come.' Mark's version adds the bitter reason: 'because they said, he has an unclean spirit.' The sin is not any insult; it is the determined refusal of the Spirit's testimony that Jesus is Lord.
Therefore I tell you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven men. Whoever speaks a word against the Son of Man, it will be forgiven him; but whoever speaks against the Holy Spirit, it will not be forgiven him, neither in this age, nor in that which is to come.Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men. And whosoever speaketh a word against the Son of man, it shall be forgiven him: but whosoever speaketh against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come.
Most certainly I tell you, all sins of the descendants of man will be forgiven, including their blasphemies with which they may blaspheme; but whoever may blaspheme against the Holy Spirit never has forgiveness, but is subject to eternal condemnation.” —because they said, “He has an unclean spirit.”Verily I say unto you, All sins shall be forgiven unto the sons of men, and blasphemies wherewith soever they shall blaspheme: But he that shall blaspheme against the Holy Ghost hath never forgiveness, but is in danger of eternal damnation: Because they said, He hath an unclean spirit.
Why it cannot be forgiven: it rejects the only way
Hebrews describes people who were once enlightened and tasted the good word of God, then fell away: 'it is impossible to renew them again to repentance; seeing they crucify the Son of God for themselves again, and put him to open shame.' A person can only be forgiven through the Christ the Spirit reveals; to blaspheme the Spirit is to insist the witness is a lie, and so to cut oneself off from the only source of cleansing. There remains 'no more a sacrifice for sins,' because the only sacrifice stands rejected.
For concerning those who were once enlightened and tasted of the heavenly gift, and were made partakers of the Holy Spirit, and tasted the good word of God, and the powers of the age to come, and then fell away, it is impossible to renew them again to repentance; seeing they crucify the Son of God for themselves again, and put him to open shame.For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, And have tasted the good word of God, and the powers of the world to come, If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.
For if we sin willfully after we have received the knowledge of the truth, there remains no more a sacrifice for sins, but a certain fearful expectation of judgment, and a fierceness of fire which will devour the adversaries. A man who disregards Moses’ law dies without compassion on the word of two or three witnesses. How much worse punishment, do you think, will he be judged worthy of, who has trodden under foot the Son of God, and has counted the blood of the covenant with which he was sanctified an unholy thing, and has insulted the Spirit of grace?For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins, But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries. He that despised Moses’ law died without mercy under two or three witnesses: Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace?
It is final rejection, not a random mistake or a struggle
John writes that there is 'a sin leading to death' and 'a sin not leading to death,' and Stephen's accusers were stiff-necked, always resisting the Holy Spirit. The Spirit's own work is to 'convict the world about sin, about righteousness, and about judgment'; to resist Him again and again is to close the door to the only light. A passing doubt, a bitter word, an angry heart: none of these is the unpardonable sin, because none of them is a settled sentence against the Spirit's testimony.
If anyone sees his brother sinning a sin not leading to death, he shall ask, and God will give him life for those who sin not leading to death. There is a sin leading to death. I don’t say that he should make a request concerning this. All unrighteousness is sin, and there is a sin not leading to death.If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death: I do not say that he shall pray for it. All unrighteousness is sin: and there is a sin not unto death.
“You stiff-necked and uncircumcised in heart and ears, you always resist the Holy Spirit! As your fathers did, so you do.Ye stiffnecked and uncircumcised in heart and ears, ye do always resist the Holy Ghost: as your fathers did, so do ye.
When he has come, he will convict the world about sin, about righteousness, and about judgment; about sin, because they don’t believe in me; about righteousness, because I am going to my Father, and you won’t see me any more; about judgment, because the prince of this world has been judged.And when he is come, he will reprove the world of sin, and of righteousness, and of judgment: Of sin, because they believe not on me; Of righteousness, because I go to my Father, and ye see me no more; Of judgment, because the prince of this world is judged.
If you fear you have committed it, you probably have not
Those who have finally rejected the Spirit do not agonize over His work; they have stopped caring. The person who fears they have blasphemed the Spirit is, in that very moment, being convicted by the Spirit about sin and righteousness. Hebrews is written to reassure its readers: 'we are persuaded of better things for you, and things that accompany salvation,' and it urges them to press on to the end. The Spirit is still working in you; receive His witness to Christ, and the door is not shut.
But, beloved, we are persuaded of better things for you, and things that accompany salvation, even though we speak like this. For God is not unrighteous, so as to forget your work and the labor of love which you showed toward his name, in that you served the saints, and still do serve them. We desire that each one of you may show the same diligence to the fullness of hope even to the end, that you won’t be sluggish, but imitators of those who through faith and patience inherited the promises.But, beloved, we are persuaded better things of you, and things that accompany salvation, though we thus speak. For God is not unrighteous to forget your work and labour of love, which ye have shewed toward his name, in that ye have ministered to the saints, and do minister. And we desire that every one of you do shew the same diligence to the full assurance of hope unto the end: That ye be not slothful, but followers of them who through faith and patience inherit the promises.
These things I have written to you who believe in the name of the Son of God, that you may know that you have eternal life, and that you may continue to believe in the name of the Son of God.These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God.
When he has come, he will convict the world about sin, about righteousness, and about judgment;And when he is come, he will reprove the world of sin, and of righteousness, and of judgment:
If anyone sees his brother sinning a sin not leading to death, he shall ask, and God will give him life for those who sin not leading to death. There is a sin leading to death. I don’t say that he should make a request concerning this.If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death: I do not say that he shall pray for it.
Therefore I tell you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven men. Whoever speaks a word against the Son of Man, it will be forgiven him; but whoever speaks against the Holy Spirit, it will not be forgiven him, neither in this age, nor in that which is to come.Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men. And whosoever speaketh a word against the Son of man, it shall be forgiven him: but whosoever speaketh against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come.
but whoever may blaspheme against the Holy Spirit never has forgiveness, but is subject to eternal condemnation.”But he that shall blaspheme against the Holy Ghost hath never forgiveness, but is in danger of eternal damnation:
For concerning those who were once enlightened and tasted of the heavenly gift, and were made partakers of the Holy Spirit, and tasted the good word of God, and the powers of the age to come, and then fell away, it is impossible to renew them again to repentance; seeing they crucify the Son of God for themselves again, and put him to open shame.For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, And have tasted the good word of God, and the powers of the world to come, If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.
If anyone sees his brother sinning a sin not leading to death, he shall ask, and God will give him life for those who sin not leading to death. There is a sin leading to death. I don’t say that he should make a request concerning this.If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death: I do not say that he shall pray for it.
When he has come, he will convict the world about sin, about righteousness, and about judgment;And when he is come, he will reprove the world of sin, and of righteousness, and of judgment: